ALD2019 Session AF2-MoP: Precursor Selection and Growth Optimization Poster Session

Since MgO has high temperature stability, wide band gap, insulating, and diffusion barrier properties, it has been studied to use as a cathode coating layer in Li-ion battery, buffer layer for superconductors, high-k gate dielectric and ferroelectric non-volatile memory, a dopant for High K capacitors, etc.

In this work, deposition of magnesium oxide (MgO) thin films was conducted with liquid precursor Bis(ethylcyclopentadienyl) magnesium (Mg(EtCp)₂) and various reactants such as H₂O, O₂ plasma and O₃ by using atomic layer deposition (ALD) method. The MgO films were analyzed by ellipsometry, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and X-ray reflectivity (XRR) to compare step coverage, chemical composition, crystallite orientation as well as film density of the films deposited with three different reactans.

ALD characteristic saturation behavior was observed for H₂O and O₂ plasma processes between 200 and 300^oC with Mg saturation pulse time 1 sec and 1.5 sec, respectively. GPC of MgO at 250^oC was 1 A/cy with H₂O and O₂ plasma processes. In the case of O₃ process, however, ALD characteristic saturation behavior was only observed above 250^oC. MgO deposition rate was constant between 200^oC and 300^oC for O₂ plasma process only. MgO deposition rate was decreased with temperature in the case H₂O process, and was increased with the temperature in the case of O₃ process.

MgO films deposited with water thermal ALD and O₂ PEALD exhibited good stoichiometric composition about Mg:O = 1 : 1 with low carbon content and excellent step coverages at the deposition temperatures between 200 and 300^oC. MgO film density with XRR was ~3.6g/cc at most deposition conditions. However, in O₃ process at 200^oC, a large amount of carbon (~ 13%) was detected, which also led to poor step coverage (~ 68%). XRR density was less than 2.5g/cc, lower than other deposition conditions. In addition, it showed no MgO XRD peak suggesting deposition of amorphous film. On the contrary, O₃ process at 300^oC showed sharp and strong MgO XRD peak with (200) dominant orientation, and film density was ~3.5g/cc, similar to H₂O and O₂ plasma processed MgO films.

In summary, we have demonstrated MgO ALD with Mg(EtCp)₂ and 3 types of reactants, H₂O, O₂ plasma, and O₃. Most conditions showed stoichiometric film composition, and good step coverage. Only O₂ plasma process showed constant ALD rate between 200 and 300^oC. O₃ process below 250^oC showed high carbon and oxygen content in the film, lower film density and poor step coverage. However, at 300^oC, similar films were deposited with all three reactants.

Titanium oxide (TiO₂) and titanium-based perovskites have been attracting attention as capacitor dielectric materials for the next-generation DRAM. Atomic layer deposition (ALD) is used as a deposition method because it can prepare conformal films over high-aspect-ratio capacitor structures. Titanium precursors capable of high-temperature ALD process were studied to produce high-quality TiO₂ films with excellent step coverage. The most common ALD precursors, tetrakis(dimethylamino)titanium and titanium tetraisopropoxide, showed low ALD temperatures due to their insufficient thermal stability. Heteroleptic titanium precursors having a cyclopentadienyl (Cp) ligand that binds strongly to titanium have been reported to increase the ALD process temperature [1]. There are two types of the titanium precursors with a Cp ligand: alkylamines having dimethylamino (NMe₂) ligands and alkoxides having methoxy (OMe) ligands. However, no direct comparison between two types of precursors and ALD processes using them has been reported. In the present study, an alkylamine-type heteroleptic precursor, tris(dimethylamino) cyclopentadienyl titanium [CpTi(NMe₂)₃], and an alkoxide-type heteroleptic precursor, trimethoxy cyclopentadienyl titanium [CpTi(OMe)₃], were comparatively studied. Ozone was used as an oxidizing agent for ALD TiO₂. The saturation doses of both precursors were measured at different temperatures to determine the ALD temperature window. The results showed that CpTi(OMe)₃ has better reactivity and thermal stability compared to CpTi(NMe₂)₃., which is explained by density functional theory calculations. Both precursors showed excellent step coverage and relatively wide bandgap at the temperature at which the thin film grows only by the ALD reaction. However, the poor step coverage and narrow bandgap were observed at temperatures at which the CVD reaction occurred due to the thermal decomposition of the precursor. Therefore, a titanium precursor capable of a high-temperature ALD process is essential, and the alkoxide-type titanium precursor is superior to the amine-type titanium precursor.

[1] R. Katamreddy, et al., in: ECS Trans., ECS, 2009: pp. 217–230. doi:10.1149/1.3205057.

There is substantial lag in the development of atomic layer deposition (ALD) processes for nitridescompared to the high-quality, conformal oxides for which ALD has become the standard. A major factor in this disparity is the ready availability of highly reactive oxygen sources (mainly H₂O, O₂, and H₂O₂). High-energy nitrogen precursors are similarly required for the efficient incorporation of nitrogen in a film. Ammonia has often been used in conjunction with metal chlorides but requires relatively high temperatures for thermal ALD. Plasma-enhanced ALD can utilize molecular nitrogen as a precursor but can reduce film conformality on complex supports and damage the underlying substrate.

Hydrazine (N₂H₄) is an alternative precursor which has been rarely explored for the fabrication of nitrides in ALD, but which is experiencing a surge in popularity due to its high reactivity, which enables the deposition of nitrides as-yet undemonstrated by ALD.¹ The added reactivity and volatility of liquid hydrazine may enable new reaction mechanisms, lower deposition temperatures, and conformality for high aspect ratio applications.

Sn₃N₄ is a metastable semiconductor which shares a crystal structure with its analog, Si₃N₄; unlike Si₃N₄, Sn₃N₄ has only recently been grown by ALD,² being synthesized much more often through reactive sputtering.³ As a binary, Sn₃N₄ has applications as a battery anode material, for photoelectrochemistry, and optoelectronic devices. We will report progress on the deposition of Sn_xN_y films from tetrakis(dimethylamido) tin (TDMASn) and N₂H₄. Growth per cycle of this material (determined by x-ray reflectivity) is 0.4 Å at 200 °C, similar to the sole report of Sn₃N₄ from PE-ALD,⁵ despite films being substantially Sn-rich. Identification of ALD growth window and self-limiting deposition characteristics are underway; initial testing indicates a competing chemical vapor deposition process which can be eliminated with adequate tuning of pulse/purge characteristics. A comparison of film conductivity and optical absorption at different growth temperatures will be presented. General issues of N₂H₄ purity and routes to prevent or control oxynitride formation will be discussed.

(1) Du, L., et al. The First Atomic Layer Deposition Process for Fe_xN Films. Chem. Comm., 2019,ASAP. DOI: 10.1039/C8CC10175B [https://doi.org/10.1039/C8CC10175B].

(2) Stewart, D. M., et al. Tin Oxynitride Anodes by Atomic Layer Deposition for Solid-State Batteries. Chem. Mater. 2018, 30, 2526–34.

(3) Caskey, C. M., et al. Semiconducting Properties of Spinel Tin Nitride and Other IV3N4 Polymorphs. J. Mater. Chem. C 2015, 3, 1389–96.

Tin oxide (SnO₂) has attracted lots of attention because of its excellent chemical, electrical, and optical properties. SnO₂ films were deposited on Si(100) substrates by home-build atomic layer deposition (ALD) using tetrakis dimethylamino tin (TDMASn) as metal precursor and H₂O as oxidant at low substrates temperature. Low temperature SnO₂ ALD process is especially important due to low thermal budget consideration for thermally sensitive materials such as organic light emitting diodes and photovoltaic cells. Thickness and refraction index of SnO₂ films were determined by ellipsometry. The surface morphology and cross-sectional image were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. As shown in Fig. 1, the growth rate of SnO₂ thin film at 150 ^oC was saturated about at 1.65 Å/cycle when TDMASn pulse time is larger than 0.7 s. The growth rate of SnO₂ thin film increased to about 2.55 Å/cycle as the substrate temperature was decreased to 50 ^oC. Top-view SEM image in Fig. 2 shows uniform SnO₂ thin films were deposited on Si wafer. Cross-section HRTEM image in Fig. 3 shows that the dense and continuous SnO₂ thin films of 32.4 nm at very low substrate temperature (50 ^oC).

ALD of dielectrics requires new precursor chemistries. Development efforts have focused on new Organometallic, Organosilicon and Organoaluminum precursors. Our research focus has been on oxidants, and specifically hydrogen peroxide reactivity. Due to this reactivity, hydrogen peroxide use may allow lower deposition temperatures and achieve distinct properties in the resulting film when compared to other oxidants. Our research study uses:

• Gas-phase hydrogen peroxide, delivered from an anhydrous, ampoule-based formulation by use of a membrane delivery system.
• High concentration H₂O₂/H₂O delivery by in situ concentration methods and use of a membrane vaporizer as a gas generator.

Initial results for ALD growth of ZrO₂ from anhydrous H₂O₂ and CpZr(N(CH₃)₃) exhibit high quality growth of film at 260° C. Minimal saturation delay and a linear growth curve were observed. XPS and XRR were used to characterize ZrO₂ composition, showing significant similarities to films grown using ozone. Subsequently, films grown using ALD and H₂O₂ were placed into MIMCAP structures, which had high k values measured at 35. This was a slight improvement over films grown with 20% ozone concentration which had high k values of 32.

Novel Gas Generator

Our approach involved development of a novel gas generator that delivers H₂O₂/H₂O mixtures. A carrier gas is connected to this generator, which delivers up to 5% H₂O₂/21% H₂O gas by volume from 30wt% H₂O₂ liquid solution (H₂O/H₂O₂=4.2). This gas mixture enables SiO₂ films to be grown at highly reduced temperature compared to water. Testing was done with tris(dimethylaminosilane) (N(CH₃) ₂) ₃SiH and H₂O₂/H₂O. SiO₂ was deposited at temperatures at least 200° C lower with the hydrogen peroxide mixture than with water.

Atomic Layer Deposition (ALD) of silicon oxide is commonly used in the semiconductor industry for its excellent thickness control and conformality. For some applications, films deposited at low temperatures with low wet etch rate or low dielectric constant (k) are required. Carbon doping is a known method to reduce the wet etch rate as well as the k value of the silicon oxide film. In this paper, ALD SiO_xC_y films were studied. The impact of oxidant concentration and deposition temperature on the carbon content, WER, k value and other properties of the deposited film, with and without post deposition annealing and post deposition hydrogen plasma treatment is discussed.

In ALD conference 2017^[1], the impact of the precursor design for the number of Si-CH₃, Si-N and Si-H bonds on the reactivity, carbon content, and dHF WER of the deposited films were reported. It was demonstrated that precursors with only one Si-CH₃ bond substitution, eg. di-iso-propylaminomethylsilane (DIPAMS), could deposit silicon oxide film with a relatively high GPC and carbon doping up to 10 at. %. In this report, a new organosilane precursor “Precursor V” is designed and it provides higher reactivity and higher carbon content and lower WER than DIPAMS, films with up to ~20 at. % C are obtained. With thermal annealing at 600 ℃, film k value reduced from ~6 to < 4, almost no etch after 10min in 0.5% dHF dip, while film carbon content showed no change, and film shrinkage was < 2%. FTIR spectra show decreased Si-OH peak, and increased Si-O-Si network peak, indicating that Si-OH to Si-OH crosslinked to form Si-O-Si linkage at 600 ℃. In contrast, by annealing at 800 ℃, the film carbon content is reduced significantly, from 17 at. % to 6 at. %, and the film density is increased from 1.5 g/cm³ to 2.0 g/cm³. A high shrinkage of ~25% was also observed from the 800 ^oC anneal, indicating a significant densification of the film with carbon removal. Direct hydrogen plasma treatment on the film was also studied. The film k value reduced from around 6 to < 4. The film develops a dense surface layer with higher WER, between 10-40 Å. However, WER of the bulk film remains unchanged compared to as-deposited film. Corresponding to this observation, the film surface carbon is reduced, but the bulk film carbon content is kept constant. FTIR shows Si-OH decrease, Si-O-Si increase, and Si-H increase, indicating crosslinking of Si-OH bonds to form Si-O-Si network and generation of Si-H bonds during H₂ plasma treatment. The hydrogen plasma treatment forms a densified SiO₂ layer with removal of carbon near surface region and protecting the bulk film from carbon depletion.

[1] M. Wang, et al. ALD 2017

Atomic layer deposition (ALD) is a vapor phase thin film deposition technique, which enables deposition of thin films with high material quality, good uniformity, high conformality, and sub-nanometer thickness controllability. Therefore, ALD has been regarded as one of the most suitable deposition technologies for semiconductor device fabrication. Since ALD is based on sequential self-limited reactions on surfaces, understanding the surface chemical reaction mechanism is crucial for development of ALD process.

ALD of Al₂O₃ has been widely investigated owing to its wide ALD temperature window, high vapor pressure of Al precursors such as trimethylaluminum (TMA), and wide applicability of Al₂O₃. It is known that the reaction between surface adsorbed precursors and reactants, and the resulting material properties of deposited Al₂O₃, are affected by the type of the oxidant. However, relatively small research effort has been focused on the chemical reaction mechanisms of each oxidants during ALD.

In this study, we investigate the reaction mechanism of various oxidants such as H₂O, H₂O₂ and O₃ during ALD of Al₂O₃ with TMA. Density functional theory (DFT) calculations at B97D3/6-311+G* level of theory were performed using Gaussian 09 suite of programs. Our results show that the methyl groups adsorbed on the surface can be oxidized into hydroxyls with all considered oxidants with ease. The number of oxidant molecules required for the reaction is one for H₂O, and two for O₃ or H₂O₂. According to the activation energy of the considered reactions, it is suggested that O₃ is the most reactive oxidant for Al₂O₃ ALD with TMA.

With scaling down of complementary metal-oxide semiconductor (CMOS), atomic layer deposition of HfO₂ is a key technology for ultra-thin and high-kgate dielectrics. To obtain high-quality HfO₂ and good devices performances, various Hf precursors, such as Hf halides, alkylamides, and alkoxides, have been employed. However, these precursors have clear limitations such as low reactivity of halides and alkoxides and poor thermal stability of alkylamids. Recently, heteroleptic precursors have been investigated as alternatives to the existing homoleptic precursors. Among them, partial substitution with a cyclopentadiene (Cp)-based ligand has been reported to control volatility and thermal stability of the precursor. Despite of the promising usages, there is still lack of systematic studies on the film properties associated with growth characteristics of ALD HfO₂ using Cp-containing precursors.This could be due to the complexity of the Cp-containing precursors, which makes difficult to conduct theoretical studies to support the growth mechanism.

In this study, we investigated the effects of substituting Cp ligands for high-kproperties of ALD HfO₂ by using Hf(N(CH₃)₂)₄ and CpHf(N(CH₃)₂)₃. The Cp ligand improved the thermal stability of precursor to withstand thermal decomposition up to 350 °C, but decreased the saturated GPC in the ALD window. The growth characteristics were discussed with the theoretical calculations utilizing geometrical information on the precursor and density functional theory. In addition, we analyzed the chemical composition such as C impurities and oxygen vacancies through XPS and the microstructure such as crystallinity, density, and interlayer through XRD, XRR and TEM. These results were comparatively studied in relation to the electrical properties of ALD HfO₂. This study can provide researchers with a broad insight to select proper precursor for the fabrication of high quality dielectric layer in future nanoscale devices.

Atomic layer deposition (ALD) of copper oxide presents a powerful opportunity to grow p-type semiconductor material for a wide variety of applications such as transparent conducting oxide, solar fuels catalysis, and power devices. There are, however, very few ALD processes to facilitate the growth of copper oxide. Cu(II) bis(dmiethylamino-2-propoxide) (Cudmap) has previously been used to grow copper metal using a reducing source such as tertiary butyl hydrazine.^1,2 Cudmap has also been demonstrated to grow Cu₂O using water as a co-reactant, self-reducing from Cu(II) to Cu(I) in the presence of water.³ This study will examine the effect of ALD co-reactants, ozone and water, on the copper oxidation state of copper oxide films grown using Cudmap.

Copper oxide films were grown in a Veeco Savannah ALD reactor using Cudmap and ozone or water at 150 °C on Si and c-plane sapphire. This is the first experimental demonstration of CuO films using Cudmap and ozone. Using ozone, a growth rate of 0.18 Å/cycle was achieved at 150 °C, far higher than the measured growth rate of 0.04 Å/cycle when growing with water. Additionally, XPS was able to confirm only the Cu(II) oxidation state with a Cu/O ratio of 1 verifying CuO films. For comparison, films grown with water show the presence of only Cu(I) oxidation state and have a nearly stoichiometric with a Cu/O ratio of 2:1. AFM also indicated uniform film growth as low as 2 nm independent of co-reactant, with CuO films grown with ozone being rougher than Cu_xO films grown with water. Initial optical and electrical properties of the films will be examined for p-type semiconductor applications.

References

(1) Väyrynen, K.; Mizohata, K.; Räisänen, J.; Peeters, D.; Devi, A.; Ritala, M.; Leskelä, M. , , 6502.

(2) Kalutarage, L. C.; Clendenning, S. B.; Winter, C. H. , , 3731.

(3) Avila, J. R.; Peters, A. W.; Li, Z.; Ortuno, M. A.; Martinson, a. B. F.; Cramer, C. J.; Hupp, J. T.; Farha, O. , , 5790.

Zirconium oxide (ZrO₂) is an attractive material with many applications because of its excellent mechanical, thermal, optical, and electrical characteristics ^1-3. ZrO₂ can present three crystalline structures, i.e., monoclinic (below 1170 °C), tetragonal (1170-2370 °C), and cubic (above 2370 °C) ¹. To synthesize ZrO₂ nanomaterials, there have to date many methods developed. ALD is a unique thin-film technique, featuring its tremendous capabilities for depositing conformal and uniform thin films with the atomic preciseness ^{4, 5}. Using Tetrakis(dimethylamido)zirconium and water as precursors, previous studies ^{6, 7} have deposited ZrO₂ on carbon substrates in the range of 100 – 250 ^oC. However, these studies have not fully investigated the growth mechanism and film characteristics of the ALD ZrO₂. Applying in situ quartz crystal microbalance (QCM), in this study we optimized growth parameters and then further studied the growth characteristics in the range of 50 – 275 ^oC. We found that the growth rate of the ALD ZrO₂ decreases with increasing temperature in the range of 50 – 225 ^oC, but the growth of the ALD ZrO₂ at 250 and 275 ^oC terminated after the first several ten cycles. Furthermore, we applied synchrotron-based techniques to study crystallinity and film thickness of the ALD ZrO₂ deposited at different temperatures, including X-ray diffraction and X-ray reflectivity. In addition, we studied the films’ composition using X-ray photoelectron spectroscopy, observed the films’ morphology using scanning electron microscopy, and analyzed the films’ structure using transmission electron microscopy. These studies provided us an integral understanding on the growth mechanism and films’ characteristics of ALD ZrO₂.

1. O. S. Abd El-Ghany and A. H. Sherief, Future Dental Journal, 2016, 2, 55-64.

2. S. Kouva, K. Honkala, L. Lefferts and J. Kanervo, Catalysis Science & Technology, 2015, 5, 3473-3490.

3. L. Yin, Y. Nakanishi, A.-R. Alao, X.-F. Song, J. Abduo and Y. Zhang, Procedia CIRP, 2017, 65, 284-290.

4. X. Meng, X. Wang, D. Geng, C. Ozgit-Akgun, N. Schneider and J. W. Elam, Materials Horizons, 2017, 4, 133-154.

5. X. Meng, X.-Q. Yang and X. Sun, Adv Mater, 2012, 24, 3589-3615.

6. J. Liu, X. B. Meng, M. N. Banis, M. Cai, R. Y. Li and X. L. Sun, J Phys Chem C, 2012, 116, 14656-14664.

A hydrophobic coating has been widely used in various applications from passivation coating on electronics to medical or even pharmaceutical devices. In many applications, organic material coatings such as fluorocarbon or hydrocarbon compounds have been used for hydrophobic coating due to their low material cost, simple coating process, and chemical stability. However, organic coatings have several disadvantages in practical applications, chiefly their inherently poor mechanical durability and thermal stability. Hydrophobicity was also found in a few inorganic metal oxides. However, hydrophobicity using inorganic metal oxide was not retained after high-temperature annealing or UV exposure because of the generation of the surface hydroxyl group. To overcome these problems, hydrophobic coating using rare-earth oxide (REO) was reported. Although its superior thermal and chemical stability, however, REO is expensive because of its scarcity and has some deleterious effects on the human body. In addition, the relatively high process temperature is an obstacle for coating on a thermally fragile substrate, such as fabric or polymer substrate. Therefore, it is highly required to fabricate a hydrophobic surface with low cost and safety material at low temperature.

Silicon oxide (SiOx) is a well-known material in semiconductor industries. Since it can be easily formed by using vapor deposition, exhibiting good chemical, mechanical, and electrical properties, it has been greatly investigated for various applications. SiOx is inherently hydrophilic material because of the presence of silanol (Si-OH) groups on the surface. Therefore, it is hard to make a hydrophobic surface of SiOx without surface treatment or functionalization.

In this study, hydrophobic ALD SiOx was obtained at the low growth temperature without any post-treatment. The water contact angle of ALD SiOx grown at 50 °C is 94 °. However, when the growth temperature is 100 and 150 °C, the water contact angles were decreased to 74 and 53 °, respectively. This hydrophobic characteristic of ALD SiOx was retained after the annealing at 300 °C. To analyze this phenomenon, various analysis including XPS and AFM had proceeded. To obtain superhydrophobicity, ALD SiOx was coated on the silicon nanowire (SiNW) at 50 °C. On SiOx-coated SiNW, superhydrophobicity is observed for water, blood, and 10 wt% ethanol solution. Owing to its low process temperature, hydrophobic SiOx can be also coated on the thermally fragile cloth, cotton or spandex, for instance, enhancing the waterproof characteristics. The detailed experimentation and origin of hydrophobicity of low-temperature ALD SiOx will be discussed.

In recent years, technologies for stacking semiconductor devices in three dimensions have been introduced as a method for overcoming the limitations of the two-dimensional scaling of devices. Thus, there is an increasing interest in atomic layer deposition (ALD) which can deposit thin films with excellent conformality in high-aspect-ratio three-dimensional patterns. In particular, SiO₂ and SiN thin films used as tunneling oxide, trap layer, and blocking oxide in 3-dimensional vertical NAND devices must have excellent step coverage in channel hole as well as good physical and electrical characteristics. In the conventional ALD processes of silicon oxide, the physical and electrical properties of the deposited thin film are improved as the deposition temperature increases, however, at high temperatures above 500°C, the thermal decomposition the Si precursor occurs, resulting in poor step coverage and film properties [1]. In the present work, we developed an ALD process using a Si precursor with excellent thermal stability, which does not cause a step coverage degradation due to thermal decomposition up to 750°C. The thermal decomposition of the Si precursor was evaluated by examining the growth rate change with the feeding time of Si precursor at 600°C or higher temperatures. The step coverage, composition, density, and leakage current of silicon oxide films deposited at different temperatures were investigated and compared with thermal oxide. The effects of the oxidizing agent on the deposition kinetics and the film properties were also investigated and discussed.

References [1] S.-W. Lee et al., Electrochem. Solid-State Lett., 11, G23 (2008).

HfO₂-based dielectrics deposited by ALD have been utilized in CMOS manufacturing since the 45 nm node [1]. In addition to applications of ALD HfO₂-based dielectrics in CMOS and DRAM, the recent discovery of ferroelectricity in HfO₂-based dielectrics [2] shows promise for applications in emerging non-volatile memory [3] and neuromorphic computing [4]. Thus, improving and modifying the growth of ALD HfO₂ is of significant industrial interest.

For ALD growth of HfO₂, H₂O and O₃ are the most commonly used oxidants. The drawbacks of H₂O include low oxidative reactivity and strong adsorption to surfaces in the deposition chamber which requires long purge times. Although the use of the strong oxidant O₃ in ALD typically uses reduced cycle times compared to H₂O, O₃ exposure can lead to unwanted oxidation of the underlying substrate which can significantly impact final device properties. In this regard, H₂O₂, which has an oxidation potential greater than H₂O but less than O₃, is an attractive candidate as an alternative oxidant for ALD growth of metal oxides.

In this study we evaluated a source for anhydrous H₂O₂ delivery which overcomes some of the drawbacks of H₂O₂/H₂O solutions, which have a low concentration of H₂O₂ in the vapor phase. The novel source and delivery system (RASIRC® BRUTE^TM Peroxide) consists of > 99% H₂O₂ dissolved in non-volatile solvent passed through a tubular membrane which is selective to H₂O₂.[5-7]

By optimizing the hardware and delivery setup to minimize vapor phase H₂O₂ decomposition and depletion effects, we were able to demonstrate uniform ALD HfO₂ growth across a 300 mm wafer in a cross-flow deposition chamber. In order to compare the performance of H₂O₂ with the other commonly used oxidants, we compared ALD HfO₂ growth with well-established processes using H₂O and O₃ [8]. Dose dependence of H₂O₂ was investigated to determine reactant saturation. Using a saturated H₂O₂ pulse we obtained > 50% increase in growth-per-cycle compared to both H₂O and O₃ while also significantly improving within-wafer-uniformity. Further optimization of purge times and carrier Ar flow rate achieved a reduced cycle time for H₂O₂ process which was > 50% less than the cycle time required for H₂O process and approaching the optimized cycle time for the O₃ process.

References

1) M. T. Bohr et al., IEEE Spectr. 44, 29 (2007)

2) T. S. Böscke et al., Appl. Phys. Lett.99, 102903 (2011)

3) T. Mikolajick et al., MRS Bull. 43, 340 (2018)

4) H. Mulaosmanovic et al. Nanoscale10, 21755 (2018)

5) D. Alvarez, Jr. et al., ALD 2014

6) D. Alvarez, Jr. et al., AVS 2015

7) www.rasirc.com/product-brute-peroxide.html

Zinc blende-structure γ-copper (I) chloride is a wide, direct bandgap semiconductor with the potential for applications in UV optoelectronics. Atomic layer deposition has previously been applied to deposition of copper chloride CuCl thin films and nanocrystallites [1,2]. The ALD-like process was reported using solid precursors [Bis(trimethylsilyl)acetylene]-(hexafluoroacetylacetonato)copper(I) and Pyridine HCl [3]. In this paper, we worked with anhydrous 1-Chlorobutane as a Cl precursor for deposition of CuCl thin films. The advantage of this liquid precursor is high vapour pressure enabling short pulsing times. The CuCl films were deposited on crystalline silicon with different pretreatment protocols and also on flexible polyimide polymeric substrates. The structural, chemical, optical and photoluminescent properties of CuCl thin films were studied by SEM, XRD, AFM, XPS, optical reflectance and photoluminescence. Figure 1 shows the SEM images of a layer of CuCl crystallites on a silicon substrate cleaned by RCA protocol and deposited using liquid 1-Chlorobutane. The deposition using a liquid 1-chlorobutane precursor is compared to the process using previously reported solid Pyridine hydrochloride precursor.

Figure 1: SEM images of a layer of CuCl crystallites on a silicon substrate cleaned by RCA protocol.

References:

[1] G. Natarajan, P.S. Maydannik, D.C. Cameron, I. Akopyan, B. V. Novikov, Atomic layer deposition of CuCl nanoparticles, Appl. Phys. Lett. 97 (2010) 241905. doi:https://doi.org/10.1063/1.3525929.

[2] P.S. Maydannik, G. Natarajan, D.C. Cameron, Atomic layer deposition of nanocrystallite arrays of copper(I) chloride for optoelectronic structures, J. Mater. Sci. Mater. Electron. 28 (2017) 11695–11701. doi:10.1007/s10854-017-6973-8.

[3] R. Krumpolec, T. Homola, D. Cameron, J. Humlíček, O. Caha, K. Kuldová, et al., Structural and Optical Properties of Luminescent Copper(I) Chloride Thin Films Deposited by Sequentially Pulsed Chemical Vapour Deposition, Coatings. 8 (2018) 369. doi:10.3390/coatings8100369.

Silicon nitride (SiN) films have been widely applied to the in solid-state devices as functional and process layers. The examples include charge trap layer in flash memory, gate dielectric layer in thin film transistors. gate spacer in FinFET transistor, etch stop layer in CMP, and capping layers in interconnection. The requirements of thin and smooth film, its uniform thickness and composition distribution, and high conformal coating on complicated structure have allowed ALD method to be widely introduced to make SiN films. In SiN-ALD process, the selection of Si precursor is significant because of the variability of film characteristics such as growth rate and material/dielectric/electrical properties. In this work, the number of Si atoms in precursor has focused on fabricating SiN-ALD films to investigate its linkage to growth and materials properties of SiN films.